Activation of the human vimentin gene by the Tax human T-cell leukemia virus. I. Mechanisms of regulation by the NF-kappa B transcription factor.

The molecular basis for transactivation of the human vimentin gene by the Tax protein from the human T-cell leukemia virus (HTLV-1) is analyzed in this report. We first demonstrate that the factor NF-kappa B binds to the vimentin promoter. Using gel retardation assays, we found the putative NF-kappa B protein. Specific antibodies and competition experiments between the NF-kappa B-binding site in the interleukin-2R alpha and HIV-1 promoters and the vimentin promoter show that the three sites have identical affinity for the factor. We further show that the mechanisms of activation of NF-kappa B by the Tax protein involve a cellular inducer. Nuclear extract from lymphoid cells expressing Tax can induce in vitro a NF-kappa B binding activity in nonlymphoid cytosolic extract. This inducer, if preexisting in an inactivate state in T-cells which are not expressing Tax, cannot be switched to an active state by addition of partially purified Tax protein. While found in the nucleus of Tax-expressing cells in our experiments, this inducer might be cytoplasmic as well. In a first attempt to identify and characterize the inducer, we present the results of fractionation assays of nuclear extract.